Abstract In the U.S., Latina women report higher rates of inactivity than their non-Hispanic White and male counterparts, and are disproportionately affected by related health conditions (e.g., cancer, hypertension, heart disease, stroke, diabetes). To address this public health crisis, evidence-based interventions that utilize state-of-the-art technology, theory and methods are needed to increase physical activity (PA) among this high-risk population. Recently, our team conducted a randomized controlled trial (N=205) to test the efficacy of a 6-month culturally adapted, individually tailored, Spanish-language Internet-based PA intervention among Latinas (Pasos Hacia La Salud, R01CA159954) vs. a Wellness Contact Control Internet Group. Increases in minutes/week of moderate-to-vigorous physical activity (MVPA) were significantly greater in the Intervention Group compared to the Control Group at 6 and 12 months (p < .01) but still did not reach levels recommended in the national physical activity guidelines. As improvements in PA in the Intervention Group were significantly associated with website use and increases in self-efficacy, enjoyment, and social support in the parent study, we used these data to inform technology and theory-supported enhancements to the intervention (i.e., text messaging and adaptive goal setting to increase website use and further targeting of the previously mentioned key psychosocial constructs) to achieve even greater increases in PA, and maintain these gains over the long term (24 months) in the renewal of R01CA159954. For the proposed study, 300 Latina women will be randomized to either 1) the original Pasos Hacia La Salud tailored Internet-based PA intervention (Original Intervention) or 2) the data driven, enhanced version of the Pasos Hacia La Salud PA intervention (Enhanced Intervention). We hypothesize that participants in the Enhanced Intervention arm will report significantly more minutes/week of MVPA than participants in the Original Intervention arm at 6 months. We will also examine the maintenance of treatment effects at 12, 18, and 24 months, as well as the costs of delivering the Enhanced vs. Original Intervention programs, and the potential mediators of the intervention-PA relationship. The proposed high- reach, low-cost intervention holds great promise in promoting and maintaining the positive health benefits of PA in the lives of Latina women in the United States.